| In the process of urbanization in China, most factories in the downtown areas in cities or suburbs of cities have been moved to the industry gardens or special zones for industry as planned. The factories located in the urban area move out successively, which leaving large amount of serious polluted land in the center of the city, and the land is a precious resource. Although it can ameliorate the quality of local air, water and noise after the enterprise being relocated, the polluted soil left behind in the process of production and development still has a long-term potential impact to the local environment. In view of this, the state environmental protection department constantly demands to have risk assessment and remediation to the contaminated land in recent years, and definitely requires to "developing environment risk assessment of recycling polluted area" in "the12th five-year plan of national environmental protection", and "prohibiting land circulation and utilization to the contaminated land without assessment and harmless treatment". Environmental risk assessment of contaminated sites has been formally incorporated into the category of our country environmental protection work.The assessment of the site basing on human health risk happened before developing the area and it assesses human health hazard risk caused by site pollutant and confirms the pollutant repair goal for the purpose of guaranteeing human health. The introduction of health risk assessment concept in site management overcomes the common character of just aiming at polluted point in traditional environmental standard management mode, which makes the requirements of the management objectives too high leading to high management cost, the deficiency of time-consuming management period and problems produced by it. Compared with traditional assessment and management mode basing on environmental standard, health risk assessment mode has its extensive superiority. Since the1980s, western countries have established health risk assessment system of polluted area which is appropriate to the reality of their own countries, to conduct the management and repair of the site.This paper first has an identification of the conception of polluted sites, analyzing and expounding the superiorities of implementing site health risk assessment and its basic theory. Secondly, it has expounded, compared and analyzed the U.S. Environmental Protection Agency ’Superfund site risk assessment guide’Risk Assessment Guidance for Superfund (RAGS) model, American Society for Testing and Materials Risk-Based Corrective Action (RBCA) model, Netherlands Ministry of Housing,Spatial Planning and the Environment CSOIL2000model and the Environment Agency Contaminated Land Exposure Assessment (CLEA) model, from aspects of the concept of the model, pollutant transport model, correlation characteristic parameter and the acceptable level of risk and so on. Then, basing on the RAGS and RBCA model, to build technical framework of China’s health risk assessment of contaminated sites and establish the method of formulating the repair desired value of site. At the same time, to revise the parameters of the model according to our country related data and materials. It applies the method established in the paper and takes typical organic contaminated site and heavy metal contaminated site as examples, to carry out site environmental survey and health risk assessment, and establish the site repair goal. At the same time, imitate rainwater to leach the repaired soil and check the rationality of the repair goal.The major research contents and conclusions of the paper are listed as follows:(1) The contaminated site is defined as the area which has potential risks or causes harm to human health and the environment as a result of piling up, storing, handling, disposing of or carrying hazardous substances in other ways such as removing. The research range is restricted to the soil and ground water at a certain depth within a certain plot of land. The basic theory of the health risk assessment is elaborated in terms of the relationships between the mechanism for humans to absorb the pollutant, the dose of the absorbed pollutant, the toxicity of chemical substances, the pollutant intake and the adverse effects on human health. The advantages of the health risk assessment are analyzed:As far as the assessment targets are concerned, the humans who are in charge of the utilization of the land are the major targets and the harm that the pollutant has caused to humans is assessed. The assessment is well-targeted. The assessment range can be an area with a complete ecological system or a plot of land with a specific purpose. It is highly flexible. The research has lasted for a long time. The technological theories and methods and criteria have been well developed. The assessment result is very accurate.(2) In the dissertation, four health risk assessment models of contaminated sites that are widely recognized abroad are described and the differences between the models are analyzed. Their differences are first demonstrated in the setting of exposure pathways:①Direct oral intake. The models of RAGS and RBCA comprehensively consider the direct oral intake of soil. The models of CSOIL and CLEA make a difference between the indoor and the outdoor situation.②Skin contact. The models of RBCA and CLEA consider the skin contact with soil outdoors. The RAGS model also considers the skin contact with contaminated surface water in swimming. The CSOIL model considers the skin contact with contaminated bath water in the bath.③Intake of soil particles. The models of CLEA and CSOIL comprehensively consider the intake of soil particles indoors and outdoors, while the models of RAGS and RBCA only consider the exposure outdoors.④Exposure from the drinking water. The CSOIL model comprehensively considers the exposure from drinking contaminated water. The RAGS model classifies the water into ground water and surface water. The RBCA model only considers drinking the contaminated ground water. It is not considered in the CLEA model.⑤Intake of pollutant steam is an important exposure pathway of volatile substances. The models of RAGS, RBCA and CLEA not only consider the indoor and outdoor situations but also subdivide different situations when the pollutant volatilizes in the topsoil, deep soil and ground water. The CSOIL model also considers the intake of the pollutant in the water in the bath.⑥Exposure from food. Except the RBCA model, all models consider it, including RAGS, CLEA and CSOIL. The RAGS model includes eating plant and fish at the same time.⑦The pollutant in the soil and air enters the ground water by the leaching of the rain water and causes pollution. The RAGS model considers the situation when the pollutant enters the ground water by vertical leaching, while the RBCA model also considers lateral migration. Since there are technical norms for the risk assessment of ground water, it is not considered in the models of CLEA and CSOIL.(3)The second difference between the models of the health risk assessment of contaminated sites is the difference in the kinetic model.The major kinetic processes involved include the volatilization of soil particles and the migration of pollutant steam. All the models in this paper carry out analysis from those two aspects. In the analysis of the volatilization of soil particles, the models of RAGS, RBCA and CLEA use the diffusion coefficient (Q/C) based on the geographical environment and weather conditions of the site, In the module of the migration of pollutant steam, the Johnson&Ettinger model is used for analysis. Due to the default soil parameter under the ideal condition in the CSOIL model, in the analysis of the volatilization of soil particles, the exposure dose is calculated by using the receptor targeted TSO concentration value, while the Volasoil model based on the concept of fugacity is used for the analysis in the module of the migration of pollutant steam. There are three aspects of principle differences between the Johnson&Ettinger model and the Volasoil model:①The difference in the calculation principle of three-phase equilibrium.②The difference in the hypothesized outdoor exposure concentration distribution in the model of the outdoor volatilization③The difference in the decomposition of the architectural structure and the migration process in the model of the indoor volatilization.(4)The difference in the exposure parameter is the third factor that causes the differences in the assessment result. Since various countries have different land use types and their contaminated sites appear in different times. Therefore, they have different considerations about the exposure scene and period. The Dutch CSOIL model divides the population exposure into seven types of scenes related to human activities.Sensitive receptors include adults and children. The harm cycle is considered to be70years of one’s whole life.The exposure period for children is6years and adults64years. The case is different in the exposure in different seasons.The British CLEA model divides the exposure scenes into three types.The targeted sensitive receptors are girls and adult females. Each year from one year old to sixteen years old is considered to an exposure period. The period from16years old to59years old and the period from60to70years old are considered to be two exposure periods. The American RAGS and RBCA models divide exposure scenes into residence and non-residence scenes generally. The harm cycle is considered from two aspects:the carcinogenic harm and non-carcinogenic harm. In terms of the carcinogenic risk, the harmful effect during70years of one’s life is considered. In terms of the non-carcinogenic harm, the harm is considered within the exposure period of30years, six years for the children and24years for the adults.(5) The situation and population distribution density of contaminated site has a large impact on the setting of site risk level. The United States RAGS and RBCA models explicitly divides the hazards of pollutants into carcinogenic risk and non carcinogenic hazards, Use the product of average unit weight intake and carcinogenic slope factor to represent the carcinogenic risk CR,10-6is recommended to be used as the carcinogenic risk level that acceptable to single pollutant, and10-4is regarded as cumulative carcinogenic risk level; use the ratio of the average unit weight intake and chronic reference dose to present non carcinogenic hazards HQ, and the acceptable non-carcinogenic risk level is measured by the standard of1. Netherlands CSOIL model using the ratio (Risk) of average daily exposure and maximum allowable daily exposure amount (MPR) to evaluate the harm degree of site contamination, when Risk≤1,illustrates the risk is acceptable; when Risk>1,illustrates the contaminated sites exist the potential health risks. In the process of establishing MPR, having considered both chemical carcinogenic effect and non carcinogenic hazards, and1is the standard of non carcinogenic hazards, and10-4is the acceptable risk level of carcinogenic effect. The risk characterization of CLEA model is similar to CSOIL model, which has a compare between average exposure and health standard value (HCV) and applies1as standard to distinguish risk. HCV is also considering the carcinogenic effect and non carcinogenic hazards of the chemicals, but the carcinogenic effect takes10-5as standard of the acceptable risk level.(6) Absorbing the systematic method, technology and standard that the United States RAGS and RBCA models have established to construct the health risk assessment technical framework of our country’s contaminated sites. In this process, first to consider the circumstance of the contaminated sites in China, and divide the site into residential land, commonland, and industrial and commercial land, and among which the residential land is further divided into urban and countryside in consideration of the characteristics of rural housing in our country. In the analysis of the route of exposure, it also considers the rural residents’ living habits. In addition to general exposure pathways, including ingesting soil by mouth, skin contact, inhaling soil particles and pollutants steam, it also needs to consider the two exposure pathways of drinking contaminated groundwater and using crop grow on contaminated land. For the migration analysis model of the pollutants, it has chosen Johnson&Ettinger model under circumstances of differential pressure driven current, and also considering the situation of soil pollutants leaching into groundwater with rainwater. Basing on the existing parameter data of site risk assessment, it has a localized revision of episodic exposure parameters, human exposure parameters, site characteristic parameters, building parameters, and soil and groundwater parameters according to the different patterns in using land. In the site risk characterization, it divides the hazard of pollutants into carcinogenic risk and non carcinogenic hazard quotient, and analyzes the uncertainty in risk assessment, and suggests having a quantitative analysis by sensitivity analysis method. In the setting of repair target, it consults the method of the Bureau of American environmental protection, namely to use the multiple relationship between the concentration value at the time when the carcinogenic risk is10-6caused by pollutants and the concentration value when the non-carcinogens risk is equal to1to determine.(7) The article targeted at the ex-service refinery site in a provincial capital which is going to be developed as a residential community and carried out a survey to its environment. Benz[a]anthracene and benzo[a] pyrene in earth are recognized as the main pollutants in the site by applying the Region9’S Regional Screening Level (RSL) of United States Environmental Protection Agency as the evaluation standard with a concentration range of0.07～24.83mg/kg and0.13-4.91mg/kg respectively. The amounts of samples exceed the corresponding standard occupy42.4%and37.9%. The main exposure pathways of sensitive group are determined as mouth-intake-soil, skin-contact-with-soil, inhalation of soil particle, and inhalation of earth pollutant steam. According to the search on the relative toxicity data of pollutants and computed the value-at-risk from carcinogenic risk and non-carcinogenic risk, the carcinogenic risk and non-carcinogenic risk of benz[a] anthracene are6.6E-05and6.87, and13.03E-05and19.08for benzo[a] pyrene, both exceeding the acceptable carcinogenic risk10-6and non-carcinogenic risk1for single substance. However, the accumulated risk of the site reaches19.63E-05and28.95. The remediation goal values of these two pollutants are deduced by taking10-6and1as the acceptable risk level, concluding0.34mg/kg for benz[a]anthracene and0.032mg/kg benzo[a]pyrene.(8) The thesis conducted a health risk assessment on a chemical contaminated site in South-central China. Comparing the environmental monitoring results to relative standards and affirming there’s extensive Sb pollution in earth with a maximum concentration as high as1262.7mg/kg, outclass the risk screening value of31mg/kg. In addition, there are54%soil samples exceed this standard, mainly concentrated on the stratum3m deep. In view of the construction planning of the site in future, children and adults are determined as sensitive population, and the considered exposure pathways are mouth-intake-soil, skin-contact-with-soil and inhalation of soil particle. Searching the existing research achievements on the environmental biological hazards effect of Sb, Sb is regarded as "possibly carcinogenic to humans, a substance without human data and limited animal carcinogenic evidence". Therefore, it evaluated the non-carcinogenic risk caused by Sb and got the result that the typical risk of the site values18.8, extreme risk of65.65, and average risk of4.94, all higher than1. Taking the95%upper confidence limit(UCL) of Sb in the site as the representative concentration, when the non-carcinogenic risk level values1, the target remediation value is computed as19.3mg/kg, lower than the initial remediation goal value of Block9of United States Environmental Protection Agency but higher than Chinese A standard.Using the site health risk assessment technical model established according to the paper to compute the determined remediation goal and then design the leaching experiment for verification. The experiment compounded the repaired simulated site soil and regarded the remediation goal19.3mg/kg as the concentration of soil pollutants. With the concentration proportion of substances in local rain, simulate the rain leaching according to the pH value of3.0,4.0,4.9,5.6and7.0, and collect leachate every3-7days for45days continuously. It witnessed3.0～7.1μg/L of Sb concentration in the leachate, better than the environmental standard of site underground water, which further indicates the practical feasibility of this research. |
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